The present invention relates to a radio communication system, and more particularly to a radio communication device comprising a portable communication device and a power amplifier device connectable to the portable communication device to amplify a transmitter output therefrom. Specifically, the present invention is concerned with a method of effecting a control such that transmitter output power level of the portable communication device is kept at a minimum level required for the power amplifier device.
In general, portable or handy type radio communication devices have restrictions in respect to a battery capacity and a heat dissipation structure. Accordingly, their transmitter output is limited to about several of hundreds of mW (milliwatt) to about several watts. Such a transmitter output is of a small value as compared to that of a radio communication device carried on a vehicle or a fixed radio communication device. In other words, in case where a larger transmitter output is needed, it is necessary to provide an amplifier device connectable to the portable communication device for amplifying its transmitter output.
The configuration of a conventional communication device designed in consideration of the above and its problems will be described in connection with the case where the communication device is applied to a mobile communication system e.g. a vehicle telephone communication.
FIG. 1 is a block diagram illustrating a mobile communication device comprising a removably fitting unit 100 serving as a portable communication device and a fixed unit 200 serving as a power amplifier device into which the portable communication device 100 is removably fitted. The configuration of these units 100 and 200 will be briefly described as follows. The removably fitting 100 is provided with an antenna 102, an antenna switch 104 coupled to the antenna 102, a duplexer 106 coupled to the antenna switch 104 to switch a signal path, a receiver circuit 108 coupled to the duplexer 106, a control circuit 110 coupled to the receiver circuit 108, a transmitter circuit 112 coupled to the control circuit 110, a synthesizer 114 to control the receiver circuit 108 and the transmitter circuit 112 in accordance with a control signal from the control circuit 110, a power amplifier circuit 116 coupled between the transmitter circuit 112 and the duplexer 106, and a telephone loudspeaker/microphone 118. Reference numeral 120 denotes a battery. The fixed unit 200 is provided with an antenna 202, a duplexer 204 coupled to the antenna 202, an RF (radio frequency) amplifier 206 coupled to the duplexer 204, a circulator 208 coupled to the RF amplifier 206 and connectable to the above-mentioned antenna switch 104, and a power amplifier circuit 210 coupled between the circulator 208 and the duplexer 204. The fixed unit 200 is further provided with a control circuit 212 capable of effecting a mutual communication with the control circuit 110 provided in the removably fitting unit 100, and an electric charger 214 coupled to a power supply circuit 216 to charge the battery 120 provided in the removably fitting unit 100, when the removably fitting unit 100 is fitted into the fixed unit 200 in order to establish an electrical coupling therebetween. Signal flows are indicated by arrow.
When the removably fitting unit 100 is connected with the fixed unit 200, a power supply in the removably fitting unit 100 is switched from the battery 120 to a battery embarked in a vehicle. As a result, the battery 120 is charged by the charger 214. At this time, since the antenna switch 104 becomes operartive, a signal is received by the vehicle antenna 202 instead of the antenna 102. Upon establishment of an eletrical connection between the removably fitting unit 100 and the fixed unit 200, signal transmission is mutually effected between the control circuits 110 and 212.
FIG. 2 shows a cirucit configuration of the conventional radio communication device C1, obtained by extracting the parts relevant to the invention from the entire system configuration shown in FIG. 1 for the purpose of facilitating the description.
As shown in this figure, the portable communication device 100 comprises an input terminal 1, an amplifier 3 for amplifying an input signal, a power detector circuit 5 connected to the output of the amplifier 3, a differential amplifier 7 responsive to the difference between an output from the power detector circuit 5 and a reference voltage supplied from an input terminal 11 to produce an output signal, and a signal converter circuit 9 responsive to the output signal from the differential circuit 7 to produce a control signal for a control of the amplifier 3. The power detector 5 may comprise a directional coupler and a diode. Reference numeral 13a denotes an output terminal. The power detector circuit 5, the differential amplifier 7 and the signal converter circuit 9 constitutes an automatic output power control circuit. The power amplifier device 200 has a circuit configuration similar to that of the portable communication device 100. Reference numerals 4, 6, 12, 8 and 10 denote an amplifier, a power detector circuit, a reference voltage input terminal, a differential amplifier and a signal converter circuit, respectively, and reference numerals 13b and 14 denote an input terminal and an output terminal, respectively. The power detector circuit 6, the differential amplifier 8 and the signal converter circuit 10 constitutes an automatic output power control circuit.
An explanation will be made in connection with a serious problem occurring in designing heat dissipation structure of the portable radio communication device when the conventional radio communication configured as shown in FIG. 2 is used.
FIG. 3 is a perspective view showing the radio communication device C1 comprising the portable communication device 100 and the power amplifier device 200 provided with the circuit connectable with the communication device 100 for amplifying a transmitter output. In addition to the connecting system shown in FIG. 3, there are proposed various methods of connecting the portable communication device 100 with the power amplifier device 200. Taking into consideration appearance, convenience in using, volume and shock-proof characteristic etc., it is preferable to connect the device 100 with the device 200 in a manner that most part or the entirety of the communication device 100 is accommodated into the amplifier device 200 as shown in FIG. 3. Accordingly, such a system is ordinarily employed.
Primarily, the portable communication device 100 is so designed as to be used in an atomospheric environment. Further, the device 100 requires appearance and weight which impose restrictions on the design of heat dissipation structure. Accordingly, when the accommodating system as shown in FIG. 3 is adopted, ventilation around the portable communication device 100 is liable to be degraded with consequent elevation in temperature, thus considerably impairing heat dissipation effect.
To be more specific, in the radio communication device C1 based on the connecting system as shown in FIG. 3, irrespective of the fact that the portable communication device 100 is solely used or it is combined with the power amplifier device 200, the device 100 is designed so as to produce the output amounting to several of hundreds of mW to several W, thus producing the same amount of heat in both the usages. For this reason, in the case of using the portable communication device 100 and the power amplifier device 200 connected to each other, the temperature elevation in the portable communication device 100 is far beyond a setting value in the case of sole use of the portable communication device. This results in not only a bad influence on various kinds of circuit characteristics but also likelihood to degrade reliability, thus producing a serious problem in the radio communication device.